1. Field of the Invention
This invention relates to cable fault tracing systems. It is concerned particularly, but not exclusively, with the detection of faults in underground cables where the outer insulation is damaged, giving rise to a conduction path from an inner metallic element to ground.
2. Summary of the Prior Art
It is known that where the insulation of an underground cable is damaged, the short between the metallic element of the cable and ground causes the signals on the cable to be attenuated or for such signals to fail to be transmitted. This problem has been described and an attempted solution offered in U.S. Pat. No. 3,991,363. Improvements to this technique have been described in UK Patent Application No. 2211621.
In the known techniques low and high frequency signals are applied simultaneously to the line. The low frequency propagates by the resistive path through the fault to the ground. The high frequency system carries synchronising information in some form of modulator.
One of the injected signals is also used to locate the buried cable and trace its route.